Electric motor



Aug. 18, 1953 C. C. HUTCHINS ELECTRIC MOTOR Filed Dec. 2, 1948 2 Sheets-Sheet 1 F/GZA. FIG. 2B.

FIG. 3.

INVENTOR.

CHARLES c. HUTCH/NS ATTORNEYS Aug. 18, 1953 c. c. HUTCHINS 2,649,561

ELECTRIC MOTOR Filed Dec. 2, 1948 2 Sheets-Sheet 2 Ea: (Ia +Ic) Ru FIG 8 (lo +lc) X0 Epo INVENTOR. HQ 2 c/ggRLes c. HUTCH/NS m "\Mkjx ATTORNEYS Patented Aug. 18,

UNITED STATES PATENT OFFICE liiziieriiz isr o mig a s E- ifi c i s, w y, a, inoni iehh sEMifis Q mran! P Ridgwaei acorporafion of Pennsylvania Amalie-slide December 2, 1948, Serial No. 63,116

This invention relates to electric motors and more specifically to alternating current motors of the single phase variety.

Heretofore it has been the practiceto provide single phase motors with commutators and armature windings for startiiig purposes; or to utilize some other means to accomplish starting. One type of means employed for starting induction motors is commonly referred to as a pole shading coil whereby one portion of each pole is wrapped with a copper strip forming a closed circuit. This shading coil acts to delay th'e'fiux passing through it so that the flux lags behind that in the uhshaded part. The combined action gives a sweeping action magnetically across the face of the pole resulting in more or less of a revolving flux. This supplies the starting torque. However, shaded pole motors are usually limited to horse power ratings from ,6 to 0 Another starting method of this general type consists of using unequal air gaps" under the pole halves to produce a somewhat similar change in reluctance. The torques soav'ailable, While rather light, do exist and some" such machines are in commercial production. While several other methods for accomplishing the result of pole shading have been advanced; none have found commercial acceptance due to their having critical inherent limitations; V

Another means employed for starting induction meters is the so-called splinphase winding comprising a main runniilgwihd'ing ind a second sttor winding generally displaced in spa'c'by 90 electrical degrees fromthe' running winding. Such motors are designedsoth'at the 'cii'rr'nt-i'n the two windings are out ofp'hase and supply fluxes displaced in space and time so es to yield a motor torque on starting-.- Continued operation on both windings results in overheating or iiieificient performance, the1'fore,theusual design calls for a centrifugal switch oh the I'n'otor to disconnect the starting winding at about 70% synchronous speed. 'Ihe'feason for this is that when such a motor is up to speed thereis a difference in phase betw%'n' the counter voltages of the rotor as reflected into each winding-alhdthe resulting voltage difference forces" current to circulate, causing not only excess heating but un balance and noise. Therefore, burn outs frequently occur in this type of motor followinga failure in operation of the centrifugal switch mechanism.

Another method-for starting isemployed in the capacitor motors which are similar to split phase motors usually having squirrel cage-rotor 8 claims. (01. tie -226) 2 windings and two stator windings mechanically displaced, one of which is connected in series with a capacitor employed for the purpose of displacing a current between the two windings; This arrangement also results in a displaced flux pattern which provides a starting torque. The condenser may or may not be disconnected when the motor rea-che's normal operating speed. In the event the capacitor is disconnected, switching means are required, and if the capacitor is not disconnected, the selection of the type of capacitor becomes critical.

There is also employed a type of motor known as repulsion-start, induction-run motor. These motors have wound rotors and commutators. Upon coming up to speed, a centrifugal mechanisnr causes the commutator bars to be shortcircuited after which the armature acts as an ordinary squirrel cage rotor. In some cases, the same mechanism is used to lift the brushes to reduce brush noise and wear during operation.

It isthe object of this invention to provide a single phase" self-starting induction motor in which no commutators are required and which will operate without the use of sliding contacts such as those usually represented by slip ring assemblies; centrifugal mechanisms or external phase displacing means.

It is well known that the simple single phase induction motor can develop no starting torque whatever but if such a machine is given an impulse in-ohe direction or the other it will accelera-te to operating speed and operate in most respects an entirely siinil'a'r Iashioh' th a polyphase machine.- The physical concepts offered to explain this action; however, have heretofore been somewhat confused and the usual expedient is to adopt the device of considering the effective superpositioning or two fields so asto be either approiiimately' at right angles" to each other as in theso-c'alledfcrossfield theory or to be revolvmg irroppositedirections without interference to each other asin' the sfo 'called revolving field theory. As a result or these spar-shoes subject has been cohsideredso 'c'ompleii'in natu that motors capable of providing self-starting features have" been generally limited" as these hereinb'efore' reviewed.

As a result or extended researches iiito the theory or oper tion or single" phase matter have diseoveredsimp e and practicalf eans {of ms; vidin' asmg e-'phase motor struafire of; a type makingtheiiiachine inherently selistaIti g ith torque values generally comparable to these" obtained" in" existing polypha'se machines? It is a further object of this invention to provide a motor structure which is sufficiently simple so as to be of great economic value and, as will be seen, makes possible a provision of a most desirable form of motor at the very minimum cost.

These and other objects of the invention particularly relating to details of construction and operation will become apparent from the following description read in conjunction with the accompanying drawings, in which:

Figure 1 is a fragmentary sectional view of a Figure 3 is a sectional view of a four pole motor stator showing one possible arrangement of coil slots;

Figure 4 is a wiring connection diagram showing the connections between the coils indicated in Figure 3;

Figure 5 is a vector time diagram of voltages and currents existing in the wiring diagram of Figure 4.- under starting conditions;

Figure 6 is a vector time diagram of certain voltages and currents existing in the wiring diagram of Figure 4 under running conditions;

Figure '7 is a vector time diagram of the voltages and currents existing in the parallel circuits alone of Figure 6 showing the adjusting of the time displacement which takes place under running conditions; and

Figure 8 is a diagram showing forward and backward components of the voltages induced in the motor primary windings as are used for torque calculations.

It is well understood that the operating characteristics of the polyphase motor depend upon the proper allocation of the relationships between certain fundamental factors such as primary resistance, primary leakage reactance, secondary resistance and secondary leakage reactance with the secondry characteristics related to those of the primary through the magnetic linkages existing between them. This magnetic linkage is often referred to as the mutual reactance.

In like fashion the operation of a single phase machine depends absolutely upon a similar proper interrelationship of these same factors. It is necessary, however, to divide the motor primary windings into two or more circuits and space these circuits or elements of the winding on the motor core with respect to each other so as to take advantage of the proper balance of the above mentiond factors.

In carrying out this invention at least two styles of primary slots are essential in effecting the desired circuit balance. In Figure 1 is shown one pole of a two pole motor stator 2 containing slots A and B in which are located winding bands a and b respectively.

The slots A containing the winding band a are shallow comparatively low leakage reactance style slots in number suitable to contain the windings a and distributed over an arc of the pole face of. The are a1 may be of any convenient extent depending upon the relative proportions of the elements but preferably will not be greater than 90 electrical degrees in the average machine and usually it will be less. For illustrative purposes one pole of a two pole winding is shown in Figure 1.

However, any number of pairs of i poles may be established by repetition and variation of the arrangement as will become hereinafter apparent.

The slots B are high leakage reactance slots containing winding band I). As illustrated these slots are set well down in the core of the stator as shown by the length of the slits 4 forming deep tooth tips as compared to the length of the slits 3 associated with the slots A which form shallow tooth tips, and high leakage reactance is obtained by making the slit narrow, or completely closing the slit as in the case of slots 6 or by fillin the slit as shown in slots 8 with bundles of steel wires or steel strips 1 El. As heretofore it has been considered undesirable to use slots of high leakage reactance in motor primaries this feature represents an extreme departurefrom normal practice and represents an important element in the present invention. These slots B with their accompanying band of winding extend over the arc (12 of the pole face. This are may be of any convenient extent depending upon the design, and while preferably it will not be greater than. electrical degrees, it may be greater or less than this if desired. The two arcs a1 and 0.2 may overlap if desired in which event at least a portion of some of the slots 13 will be located beneath slots A.

It will be evident that the arrangement may be carried out in various ways; however, the essential to be provided resides in the provision of greater leakage reactance in the winding band of slots B as compared to the leakage reactance of the winding band of slots A. The primary space angle {is the distance in electrical degrees between the center lines of winding bands a and b may be 90 electrical degrees, but depending upon the values of a1 and a2 and the overlap of slots A and B will be a greater or lesser angle selected to be favorable for starting purposes and construction convenience.

In carrying out the details of the invention it is not necessary to use a sine distribution for the windings. Sine distributions are generally used in single phase machines because of the prevailing idea that noise in operation is caused by harmonics or multiple fields. A pure sine distribution would contain no harmonics or multiples, therefore a near approach would silence an otherwise noisy motor. The winding distribution as shown in the present specification results in a breaking up effect of possible multiple fields. This freedom from strict adherence to the conventional sine distribution allows the use of punchings over a wider range and considerably simplifies the problems of winding distribution from the standpoint of both manufacturing and design, with a resultant reduction in cost.

It is sometimes desirable for design purposes, as is hereinafter made clear, that the winding 1 band 17 consists of fewer conductors than the winding of band a, while at the same time the arrangement of the slotting is such that the leakage reactance of the winding in slots B is greater than the leakage reactance of the winding in slots A. In addition, the winding of band b is to have lower resistance than the winding of band a. Those skilled in the art will recognize that the fewer turns of the winding of band b when used provide a higher inverse value of transformer ratio with the rotor for this winding than the similar ratio for thewinding of the band a, thus the relative magnitudes of the countervoltages in the two windings may be adjusted by varying the number of turns of the windings. While, as previously stated, it is sometimes desirable that the winding band b have fewer conductors than the winding band a, by proper selection of the position or spacing of the a1 and b2 windings relative to the polar reference center lines as indicated in Figure 3 the winding band bmay be made with a greater number of turns of conductors than the winding band a and still provide balanced internal voltages, as will be hereinafter described, substantially eliminating circulating currents within the windings during normal running operation of the motor.

To provide the most favorable motor the winding a is laid out first and proportioned to have the lowest value of leakage reactance readily obtainable and compatible with the machine proportions selected. This winding a is proportioned to have a value of resistance such that when carrying loads at full speed the operating copper loss will be satisfactorily low from an efficiency and heating standpoint. The ratio of leakage reactance b resistance of winding a should be generally of the order of 1:2. It may be somewhat more or less than this ratio in certain designs depending upon the finally selected balance of the elements. In the winding b the ratio of leakage reactance to resistance, taking into account the lesser number of; turns and: the consequent larger conductor sizes permissible, will be generally of the order of, 211. While it, may be somewhat more or less than this ratio, the important point is that the relative relationship of this ratio of leakage reactance to resistance be generally reversed as compared to the ratio existing in winding a. Asthe ratio of leakage reactance to resistance of the winding 1) is contrary to the normal expectationin a winding of fewer turns or lesser number ofslots, it is seen that the controlling factor lies in the arrangement of the primary slots toefiectthis reversed-ratio. The slots B therefore are normally. provided with adeep narrow slit l, where, the depth of. the slit is many times greater than, the. width of the opening of the slit.

In order to avoid unexpectedreversals or other undesirable saturation effects such as occurwhen starting currents arelarge as atstaind still when the reactance values cannot ;be maintained proportional the use of the deep .-slit;. previouslyvv cone iined to secondary slotdesigmis mostimportant to provide paths for the leakageflux. Iniact, the failure of some of the:structuresdisclosed in the prior art for thepurposeof accomplishing self starting of singlephase motors resides-in the fact that these structures do-not make provision for the avoidance ofsuchsaturation effects. T erefore, the verydeep tooth tips not heretofore found on stators-due to the utility of them not having been understood-are employed in the present motor. As mentioned previously, however, the resultant required-ratiosbetween primary windings may be obtained inother ways even in manners less, easily controlled as, for example, fully closed'slots 601' the set down slots 8 shown in Figures 2A and B'or otherwise, the important factor being the reversed relationship or the ratio of leakagereactancetc resistance between the shallow. bedded windings a andthe deep bedded windings b.

It should be observed thatan-essential of=the present invention resides .in making possible the use of the. motor primaryrwinding for-:the additional purpose of causing it to formian-dnternal phase distributing device thus enabling the motor to become a self-starting machine.

The structure hereinbefore disclosed has been that of one polev of a two pole motor. If the phase angle. adjusting feature is carried further than illustrated in Figure 1, it is possible to space the paralleled sections of the windings at angles from generally 0 to 180 electrical degrees. While such extremes of construction would produce somewhat inferior motors, it is quite possible to construct motors which will operate particularly if adjustments of relative turns of the various windings are made to compensate for the particular angle selected.

The. structure as drawn in the figures shows the motor primary windings carried by the stator. It is, of course, obvious that it is equally possible to have the primary windings carried by the rotor if, for reasons of application, such a construction becomes desirable.

An additional modification is that of employing more than two windings per pole. It is entirely practical to employ a greater number of windings having the'proper relative values of resistance and impedance.

The secondary winding to be used with the above described primary winding may be a common single squirrel cage of the normal variety or any form of double squirrel cage, deep bar secondary or wound rotor arrangement.

In carrying out thedetails of this invention it is important to secure the proper balance of the elements involved. In Figure 3, which is drawn to indicate a complete four pole motor including a stator 2, a rotor 12 and squirrel cage rotor conductor bars i l; the spacing of the slots is selected on a uniform basis so that the space angles concerned can be selected and identified. Irregular spacing might be used if properly carried out but such a construction would produce a motor of less desirable characteristics than one in which the spacings wereregular. Thus the two center lines CL! and GL2 are established 180 apart or, in this case, mechanical degrees apart and the winding bands in and 112 are located on these center lines so that a set of coils is centered on each. The in coils, for example, are on the left and the (t2 coils are on the right. These bands of winding may occupy one or several slots as may be convenient for construction or design purposes. The reason'for using this winding arrangement 01' its equivalent is to bring the a2 and b1 winding sections on separate poles of the motor so that the ca sections may be connected in parallel withthe in sections, these being circuits having generally inverse resistance and reactance as hereinbeiore explained, and a further reason being to arrange that the countervoltages generated in these circuits while the motor is running will be more nearly equal and more nearly in-phase to allow continuous connection in the circuit.

Section a1 and b2 are located mono or more additional slots, the (11 bands being ahead of the bi bands in space position while the b2 bands are behind the az bands, the rotation being selected as clockwise in this figure. Obviously by shifting the position of the an and b2 bands the reverse rotation will result. Four poles alternate- 1y north and south are established'by' the flux linkages as indicated.

The winding bands are connected in seriesparallel as shown in Figure 4. It is obvious, however, that other combinations of connections can 'b'exused. providedithe relativeerelationships required are maintained. For starting purposes it is essential that the currents in the a coils reach their instantaneous maximums ahead of the occurrence of the maximum currents of the b coils to give a sweeping flux action across the pole faces thereby establishing conditions for developing starting torque. It is also essential for proper running conditions after the motor has been started that circuits in parallel have very nearly equal and in-phase countervoltages set up by the rotor if circulating currents are to be minimized.

Figure is a vector time diagram of the voltages and currents existing in the series-parallel connections shown in Figure 4 under starting conditions. It will be noted that the Ia currents, that is both Ia]. and Ia2, lead in time and space the Ibl and Ib2 currents provided the resistance and leakage reactance of the winding bands are properly established as has been previously explained.

These :2 and b current bands are located on the motor primary which may, of course, be either the stationary or rotating element of the motor, so that in each pole the fiux sweeps across the pole face in the direction of desired starting rotation.

The angle between Iaz and Ib2 is shown as a 62, whereas the angle between In and Ibi is 61. As this diagram is a well known standard representation of a series-parallel circuit it requires no further explanation beyond pointing out that the applied voltage E has two components E1) and E5. E is the voltage across the parallel branch and Es the voltage across the series branch. These voltages are at a phase angle depending upon the circuit factors as is usual. The primary power factor angles under the starting conditions are marked as 0 with subscripts referring to the various currents involved. The rotor power factor angle, that is the angle between the induced rotor voltage and current, is not shown, but it is, of course, different from that of the primary as it is determined by the rotor factors. This angle is the same under both pole halves or sections.

When the motor is up to speed, that is at the end of the starting process, the factor of rotor developed countervoltage due to rotation is approximately at a maximum. Figure 6 is illustrative of this condition. It is to be seen that, whereas the external applied voltage on the parallel part of the circuit remain constant, the countervoltages developed in a2 and bi are forced to be very slightly out of phase by the leakage reactance and resistance values. As these countervoltages Es and Eb are developed in coils located on the machine at or nearly at identical phase positions and connected in additive fashion a slight circulating current is required to bring them into phase adjustment. In order to minimize the amount of this it is merely necessary to adjust the resistance and reactance factors relative to each other or to change the relative values of turns in the as and in sections of the windin in the direction such that balance results.

The process is illustrated in Figure 7 with a diagram of the parallel circuit portion of Figure 4 redrawn to represent the current and voltage conditions with respect to each other. Hence, the two countervoltages B's and E's. are shown in opposite directions representing the fact that each tends to send a current around the circuit in a direction in opposition to the other. Figure 7 exaggerate the conditions for the sake of clearness showing .Eb greater than E's. hence the vector difference E's-E21 tends to send the current IO around the loop. Summing the corresponding applicable values the current in the b1 leg becomes Ibi-l-Ic and in the (12 leg Ia2+Ic. These summations must consider proper phase relationships of the vector quantities involved. This adjustment is made in such a way as to reduce the current in the a2 leg which has the greater resistance and. usually the lesser section and to increase the current in the b1 leg which has the lowest resistance and the greater capacity for carrying high current with the least heating. In a well balanced design the effect described is small, more especially as the current Values with the motor at full speed are much reduced, as has been hereinbefore explained.

It is now plain that for proper arrangement of the invention the poles may be handled in pairs, or groups, thus all speed combinations above the two pole speed are accounted for.

Two pole motors, however, become a special case wherein the process is identical with the exception that the series leg of Figure 4 may be dropped out for one arrangement.

It will now be obvious to those skilled in the art that by properly combining reactance and leakage reactance and resistance values in accordance with this invention and interconnecting the resulting winding bands as taught herein to provide a starting distribution which later degenerates toward an in-phase condition for running, that a very useful self-starting single phase motor structure results. It is also apparent that the Figures 3, 4, 5, 6 and 7 are diagrammatical of the means employed to accomplish this result, and that other and more or less complicated circuits than that illustrated in Figure 4 may also be employed without deviating from the invention involved herein.

Placing the three branches of the winding arrangement of Fig. 4 in series connection would result in much Weaker starting performance and would require the use of tapered resistance in the rotor winding to provide the proper variation across all pole faces. While such a motor could be made to operate, its performance would be inferior to that employing the more preferable arrangement.

It is also possible to connect the three branches in parallel and by providing proper turn adjustment the phase distributing action will provide starting torque. It will be noted that in Figure 3 the coil in is retained in a deep slot. The only reason for this is to help control the total inrush current. The coil b2 could equally well be placed in a shallow slot, as is the coil (1.1. So far as phase is concerned, the a1 coils are ahead of the pole axis of like polarity and by the same angle that the b2 coils are behind it. This means that when the motor is up to speed the countervoltages generated in these turns can be made to be exactly in phase with the voltages of like character generated in the turns of a2 and Zn. In addition, if E is set equal to E5 the branches may be placed in parallel. In the event that this is done, the factors of this (11, b2 branch must be adjusted to give the same relative position as that in Figure 5 with respect to a2 and In. It will be readily understood that a three parallel connection for a four pole motor is entirely inconsistent with the practice found in the prior art, and the fact that such a motor will operate when constructed as disclosed herein is further evidence of the extreme novelty involved in this invention.

The teachings herein are new in that it has been previously practically universally taught that it is impossible to construct a. motor of the single phase self-starting type employing a single continuously energized winding.

It is now obvious that a motor constructed in accordance with this invention utilizes a lesser number of coils than a motor constructed in accordance with previously known principles. In the present motor there is utilized one winding continuously energized, containing the full cop per requirements for operation and also entirely capable of producing a positive reliable starting with adequate torque values. This great reduction in the number of coils required. in the motor winding greatly reduces manufacturing costs While at the same time the motor retains its entire adequacy for service.

It will be recognized that in Figure the two currents Ia and Ib under starting conditions are the inrush currents and consequently are of much greater magnitude to the normal operating currents, hence the accompanying Ix and Ir drops are much exaggerated over those of normal operation. It will be also noted that the relative values of Xa and Ra, and Xb and Rb are of the required inversely proportional values hereinbefore reviewed. The flux of the motor under this condition is single in character and established as a stationary single phase field by the combined action of all the windings taken together. The vector diagram of Figure 5 is a time diagram and refers to the conditions in windings a and b as viewed from the motor terminals. A part of each of the various Ia. and Ib currents is used in establishing the magnetic flux of the motor while the remainder is transferred to the rotor as in a short circuited transformer. As the motor resembles a short circuited transformer under this condition of voltage applied with motor rotor at standstill, the mutual flux and hence the magnetizing components mentioned will be quite small. For purposes of simplifying the explanation it will be assumed that the magnetizing components are negligible, thus the Ia and Ib currents may be considered as representing the secondary components. In an actual motor calculation this difierence must be included but as can be readily appreciated for explanation purposes the'extra complication of the mary values reduced by the standstill transformer ratio. Also each of these voltages is accompanied by its secondary current Ias and Ibs, each of these being increased by the applicable transformer ratio. Each secondary current lags its voltage by an angle depending upon the ratio of the secondary resistance to impedance. The voltages are, however, out of time phase by the time angle fit existing between the primary voltage components as indicated in the vector diagram of Figure 5 or 8.-

Assuming a simple two pole motor having winding as illustrated in Fig. 1 connected as shown in the parallel portion of Fig. 4. The power betransierred to the secondary from each winding acting as a transformer is therefore the product of voltage, current and power factor. Thus it is Elsi. cos Gas for winding a and EbsIbs cos 017s for winding 1; (s signifying secondary). It should be noted that the rotor power factor angles change for each change in speed or during acceleration. Under starting conditions with large starting currents the reactance and resistance drops will be large and the angle [fa will be comparatively large, whereas under running conditions the currents Ia and Ib become reduced in magnitude whereupon the resistance and reactance drops will be reduced and the voltages E'a and E's in the diagram increase and draw together reducing the angle in as the motor comes up to speed as shown in Fig 6. This means that the angle of distribution under running conditions is minimized. Thus the means for adjusting the internal phase angles of a single phase motor to give a phase distributing operation during the starting cycle and in-phase operation of the sections during running constitute an essential part of the invention. Thus, it can be seen that the problem of proportioning involved is to provide set starting conditions and at the same time arrange relationships to provide running conditions which are satisfactory.

In order to determine the starting performance use is made of the convention that single phase currents and voltages may be considered as being composed of equal half values Which are rotating in opposite directions at a synchronous speed corresponding to the applied frequency. It is necessary to adopt this expedient at this point in order to bridge the transition from stationary pulsating eiiects to equivalent rotary values. Thus we have two secondary voltages not in time phase and two secondary currents not in time phase and each consisting of half components rotating in opposite directions. The torque developed will correspond to the combined effect of the forward components minus the combined effect of the backward components. In order to make this combination properly it is necessary to consider the space relationships of the a and b windings.

.t is quite obvious that when all windings are carrying current both the stator and rotor are threaded by a common fiux. The rotor voltages due to transformer action in accordance with this flux are out of phase with each other by the time angle Br. Also they are out of phase in their space location on the machine by the angle [35. In order to obtain a combined effect account must be taken of both time and space angles.

At the instant at which the voltage E's induced in winding a is a maximum the two components of half value Eat (forward) and Eat (backward) are together in time and also together in space on .re machine. Thus the induced voltage in winding a is the arithmetical sum or" its half components. At this same instant the induced voltage E's in winding 13 is less and Elb will reach its maximum later when its own components Ebf Ebb come together. This happens at a time angle later than the occurrence of the maximum voltage value of E's. Hence the forward and backward half components of induced voltage in winding 1) are represented in diagram of Figure 8 with each half component at the angle fit from maximum position with the directions of rotation as indicated so as to bring E's to a maximum time fit degrees later than E'a.

Crossing to the secondary side, the induced voltages E and Ebs are thus located on the motor at the angle as in space degrees. The flux, however, is a common flux. Adding these values, which have positions similar to the positions of E2. and E's shown in Fig. 8, by use of the cosine law to determine the resultant forward and backward secondary circuit components gives the fol- In a similar way the total forward and backward currents are determined again establishing winding a as the reference. Here, however, the mmfs. as represented by the currents do not combine at the same space angle as does the common flux, hence the space angle enters, this gives:

cos c,

2 2 Ia 3 aa ba COS (l s'i'l t) As the current in the rotor lags the voltage in the rotor by the power factor angle of the rotor circuit this eiiect must also be included. This gives:

Forward power=E,-,I,-, cos 0,:

but

fa E cos 0,=

I-Ience Power forward In like manner Power backward:

2 2 a| In 00S e The net power in a forward direction available for torque is the difference between the forward power and backward power.

Obtaining the torque in lb. ft. the usual conversion gives:

variably present in single phase machine At first glance the average torque expression indicates the most favorable space angle or value of a; to be electrical degrees (sin=1), however, it will be apparent that a shift in this angle to a value greater than 90 or less than 90 will affect the value as the sine of ps and advantage be taken of this fact in assembling the structure.

Under starting condition of zero speed having a second winding at a selected space angle to a first winding and applying currents of different time phase to the two windings provides a resultant forward component of torque. This is the action of the normal split phase motor in starting. When the two windings are designed to have the reversed ratio of R to X with respect to each other, the time angle between the voltages of the two windings will diminish as the currents therein diminish from starting values to running values.

As the motor starts by the use of the hereinbefore described internal phase distributing arrangement the time angle between the various windings changes but the space angle remains fixed by the location of the coils. Under running conditions the motor operates as a plurality of single phase motors located in parallel on the same structure, dividing the load in the ratio of impedances and each winding supplying part of the necessary total magnetization to provide the single common rotary flux. The primary impedance ratios remain very nearly fixed with respect to each other, being established in a fixed frequency part of the circuit. This form of motor is therefore capable of being operated over a voltage range of from just above zero to somewhat over normal without encountering sudden reversals or other unexpected similar defects in operation such as are quite common in motors depending upon reluctance variations for basic operation.

It will be apparent that the two windings connected in parallel and having inverse ratios of resistance to reactance, as shown in connection with Figure 1 and as shown in the Ep portion of Figure 4, constitute a basic element of this invention. This element may be used in conjunction with conventional coil windings, or the element may be used in conjunction with any number of similar elements by superimposing or by the procedure well known in the art called cascading.

It will also be obvious that when reference is made in this specification to distribution of winding over pole faces, the meaning to be conveyed is that the winding is distributed over the pole faces on which the winding appears and is not to be limited as meaning that each winding is necessarily distributed over the face of each pole of the machine.

The invention, as disclosed herein, may also be applied to the single phase synchronous motor. The single phase synchronous motor is no more capable of starting itself than is the single phase induction machine, but inasmuch as its starting operation is that of partially imitating the induction machine it is clear that the present invention may be used to supply the starting feature for this type of motor.

It will be understood that it is not intended that this invention shall be limited by the above description and the accompanying drawings, since it will be appreciated that various modifications may be made therein without departing from the scope oi the nve t on,

What I claim and desire to protect by Letters Patent is:

l. A self-starting single phase alternating current electric motor including a plurality of pairs of poles, a main running winding distributed over each of said pairs of poles and dis ributed over only a portion of each of the poles of at least one of said pairs of poles, and a starting winding having high leakage reactance with respect to running winding, said starting winding distributed over the portions of the poles not covered by said main running winding, v id starting winding being in series connection and n mutually inductive relation with the portion of the running winding distributed over the same polar areas therewith, and being in parailel connection with a portion of the running winding distributed over other or" said pairs of poles.

2. A self-starting single phase alternating current electric motor including a rotor member, a stator member and an air gap therebetween,-one of said members containing a plurality of winding slots, and winding coils distributed in said slots defining polar areas, said coils including coils of a running winding and coils of a starting winding, the coils of the running winding being distributed in slots over each polar area and over only a portion of at least one pair of polar areas, the coils of the starting winding being distributed in slots over the portions of the polar areas not carrying coils of the running winding, the coils of the starting winding being in series connection with the coils of the running winding distributed over the same polar areas as the starting winding and being mutually inductive therewith, and the coils of the starting winding being in parallel connection with coils of the running winding distributed over other polar areas, the coils of the starting winding having high leakage reactance with respect to the coils of said running winding, said windings being distributed and having relative turn ratios such that the time phase differences between the currents in the starting and running windings will provide starting torque and that the countervoltages induced in the parallel pair of windings will approach a substantially inphase condition with respect to each other as the motor speed approaches normal operating speed.

3. A self-starting single phase alternating current electric motor including a rotor member, a stator member and an air gap therebetween, one of said members containing a plurality of winding slots, and winding coils distributed in said slots defining polar areas, said coils including coils of a running winding and coils of a starting winding, the coils of the running winding being distributed in slots over each polar area and over only a portion of at least one pair of polar areas, the coils of the starting winding being distributed in slots over the portions of the polar areas not carrying coils of the running Winding, the coils of the starting winding being in series connection with the coils of the running winding distributed over the same polar areas as the starting winding and being mutually inductive therewith, and the coils of the starting winding being in parallel connection with coils of the running winding distributed over other polar areas, the coils of the running winding being distributed in conventional motor winding slots and lying substantially adjacent to the air gap between the stator member and the rotor member and having relatively low leakage reactance, and the coils of the starting winding being disposed in winding .slots bedded deeply with respect to the slots carrying the running winding, the starting winding lying a substantial distance from the 'airgap and having relatively high. leakage 'reactance, said windings being distributed and having relative turn ratios such that the'time phase differences between the currents .in the starting and running windings willprovide startingtorqueand that the countervoltages induced in the'parallel pair of windings will approach a substantially inphase condition with respect to each "other as the motor speed approaches normal operating speed.

4. A self-startingsinglephase alternating current electric .motorincluding a rotor member, a stator member and an'airgap therebetween, one of said members containing a plurality of winding slots, and winding coils distributed in said slots defining polar areas, said coils including coils of a running winding and coils of a starting windings, the coils'of the running winding being distributed in-slots over each polar area and over only a portionof at least one pair of polar areas, the coils of the starting'winding being distributed in slots only over the polar areas only partially covered by the starting winding, the coils of the starting winding being 'in series connection with the coils of the running winding distributed over the same polar areas as the starting winding and being mutually inductive therewith, and the coils of the starting winding being in parallelv connection with coils of the running winding distribute-d over other polar areas, the coils of the running winding being distributed in conventional motor winding slots and lying substantially adjacent to the air gap between the stator member and the rotor-member and having relatively low leakage reactance, and the coils of the starting winding being disposed in winding slots bedded deeply with respect to the slots carrying the running winding, the starting winding lying a substantial distance fromthe air gap and having relatively high leakage reactance, said windings being distributed and having relative turn ratios such that the time phase 'diiferenees between the currentsin the starting and running windings will provide starting torque and that the countervoltages induced in the parallel pair of windings will approach a substantially inphase condition with respect to each other as the motor speed approaches normal operating speed.

5. A self-starting single phase alternating current electric-motor including a rotor and a stator, said stator containing aplurality of winding slots and winding coils disposed in said slots defining polar areas, said coils including coils of a pair of windings in parallel connection, the first of said pair of windings being distributed in slots over only part of each of a first pair of polar areas, theseoond of said pair of windings being distributed in slots over only part of each of a second pairof polar areas, the first of said of windings being disposed in conventional motor winding slotsand lying substantially adjacent to the surface of the stator adjacent to the rotor and having relatively low leakage reactance, the second of :said pair of windings being disposed winding slots bedded deeply in the stator with respect to the slots carrying the first of pair of windings, the second of said pair of windings lying with the entire winding in the deep slots being a substantial distance from said surface of the stator and having relatively high leakage reactance, said coils also including a winding in series with said parallel pair of windings and being distributed in slots over the part of each of said first and second pairs of polar areas not covered by either of said parallel pairs of windings, the windings extending over each of polar areas being in mutually inductive relation, said windings being distributed and having relative turn ratios such that the time phase differences between currents in the parallel pair of windings during motor starting will provide starting torque and that the countervoltages induced in the parallel pair of windings will ap proach a substantially inphase condition with respect to each other as the motor speed approaches normal operating speed. 7

6. A self-starting single phase alternating current electric motor including a rotor and a stator, said stator containing a plurality of winding slots and winding coils disposed in said slots defining polar areas, said coils including coils of a pair of windings in parallel connection, the first of said pair of windings being distributed in slots over only part of each of a first pair of polar areas, the second of said pair of windings being distributed in slots over only part of each of a sec ond pair of polar areas and having a lesser number of turns and a lower overall. resistance than the first of said pair of windings, the first of said pair of windings being disposed in conventional motor winding slots and lying substantially adjacent to the surface of the stator adjacent to the rotor and having relatively low leakage reactance, the second of said pair of windings being disposed in winding slots bedded deeply in the stator with respect to the slots carrying the first of said pair of windings, the second of said pair of windings lying with the entire winding in the deep slots being a substantial distance from said surface of the stator and having relatively high leakage reactance, said coils also in cluding a winding in series with said parallel pair of windings and being distributed in slots over the part of each of said first and second pairs of polar areas not covered by either of said parallel pairs of windings, the windings extending over each of said polar areas being in mutually inductive relation, said windings being distributed and having relative turn ratios such that the time phase differences between currents in the parallel pair of windings during motor starting will provide starting torque and that the countervoltages induced in the parallel pair of windings will approach a substantially inphase condition with respect to each other as the motor speed approaches normal operating speed.

'7. A self-starting single phase alternating current electric motor including a rotor and a stator, said stator containing a plurality of winding slots and winding coils disposed in said slots defining polar areas, said coils including coils of a pair of windings in parallel connection, the first of said pair of windings being distributed in slots over only part of each of a first pair of polar areas, the second of said pair of windings being distributed in slots over only part of each of a second pair of polar areas, said coils also including coils of a pair of windings connected in series with said pair of windings in parallel connection, the first of said windings in series connection with the parallel pair of windings being distributed in slots over the part of the pair of polar areas not covered by the first of said pair of windings in parallel connection, the second of said windings in series connection with the parallel pair of windings being distributed in slots over part of the pair of polar areas not covered by the second of said pair of windings in parallel connection, the first of said pair of windings in parallel connection and the second of the pair of windings in series connection therewith being disposed in conventional motor winding slots and lying substantially adjacent to the surface of the stator adjacent to the rotor and having relatively low leakage reactance, and the second of said pair of windings in parallel connection and the first of the pair of windings in series connection therewith being disposed in winding slots bedded deeply in the stator with respect to said conventional winding slots and the windings lying with the entire winding in the deep slots being a substantial distance from the surface of the stator and having relatively high leakage reactance, the windings extending over each of said polar areas being in mutually inductive relation, said Windings being distributed and having relative turn ratios such that the time phase differences between currents in the parallel pair of windings during motor starting will provide starting torque and that the countervoltages induced in the parallel pair of windings will approach a substantially inphase condition with respect to each other as the motor speed approaches normal operating speed.

8. A self-starting single phase alternating current electric motor including a rotor and a stator, said stator containing a plurality of winding slots and winding coils disposed in said slots defining polar areas, said coils including coils of a pair of windings in parallel connection, the first of said pair of windings being distributed in slots over only part of each of a first pair of polar areas, the second of said pair of windings being distributed in slots over only part of each of a second pair of polar areas, said coils also including coils of a pair of windings in series connection connected in series with said first pair of windings in parallel connection, the first of said Windings in series connection with the parallel pair of windings being distributed in slots over the part of the pair of polar areas not covered by the first of said pair of windings in parallel connection, the second of said windings in series connection with the parallel pair of windings being distributed in slots over part of the pair of polar areas not covered by the second of said pair of windings in parallel connection, the first of said pair of windings in parallel connection and the second of the pair of windings in series connection therewith being distributed in conventional motor winding slots and lying substantially adjacent to the surface of the stator adja cent to the rotor and having relatively low leakage reactance, and the second of said pair of windings in parallel connection and the first of the pair of windings in series connection therewith being disposed in winding slots bedded deeply in the stator with respect to said conventional winding slots and the windings lying with the entire winding in the deep slots being a substantial distance from the surface of the stator and having relatively high leakage reactance, the windings extending over each of said polar areas being in mutually inductive relation, said windings being distributed and having relative turn ratios such that the time phase differences between currents in the parallel pair of windings during motor starting will provide starting torque and that the countervoltages induced in the parallel pair of windings will approach a substantially inphase condition with respect to each 17 other as the motor speed approaches normal op- Number erating speed. 924,725 CHARLES C. HUTCI-IINS. 1,758,191 2,219,702 References Cited in the file of this patent 5 2,479,329

UNITED STATES PATENTS Number Name Date Number 416,193 Tesla Dec. 3, 1889 379,092 598,092 Heyland Feb. 1, 1898 10 Name Date Bergman June 15, 1909 Dom May 13, 1930 Schurch Oct. 29, 1940 Ellis Oct. 16, 1949 FOREIGN PATENTS Country Date Italy -7 Mar. 11, 1940 

